Multiple channel modules and bus systems using same

ABSTRACT

Various module structures are disclosed which may be used to implement modules having 1 to N channels. Bus systems may be formed by the interconnection of such modules.

CO-PENDING APPLICATIONS

This is a continuation-in-part of U.S. patent application No.09/568,424, filed May 10, 2000.

FIELD OF THE DISCLOSURE

The present invention is directed to bus systems. More particularly, thepresent invention is directed to a bus system including one or moremodules implementing one or more communications channel(s).

Conventional bus systems are typically implemented in single channelarchitectures. While conventional bus systems have been implementedusing modules, the modules in such systems have merely been arranged ina serial relationship on a motherboard. For example, consider the bussystem shown in FIG. 1. This bus system is characterized by a master 11mounted on a motherboard 10. A number of connectors 13 are also mountedon motherboard 10. Each connector 13 is adapted to receive a module 14comprising one or more integrated circuits 15. Thus, by means of aconnector 13, a module 14 is mechanically mounted and electricallyconnected within the bus system.

One or more bus(es) 16 forms the communications channel between master11 and a termination resistor 12. Bus 16 typically comprises a number ofsignals lines communicating control information, address information,and/or data. The signal lines forming bus 16 traverse the motherboardand/or the modules to electrically connect the integrated circuits 15 tomaster 11.

There are numerous problems associated with such conventional bussystems. For example, the serial arrangement of the connectors andassociated modules creates a relatively lengthy communications channel.Since there are many factors limiting the maximum practical length of acommunications channel, channel length should, wherever reasonablypossible, be minimized.

Conventional bus systems are also characterized by numerous electricalconnection points between the connectors and the bus portions traversingthe motherboard, between the modules and the connectors, and between theintegrated circuits and the bus portion traversing the modules.Improperly matched electrical connections often produce impedancediscontinuities which tend to degrade signal transmissioncharacteristics on the bus. Accordingly, the number of impedancediscontinuities associated with the bus connections should be minimized.

Such conventional bus systems present a very static architecture whichmay not lend itself to the efficient utilization of available spacewithin a larger system. For example, a maximum, pre-set number ofconnectors is typically provided within the conventional bus system,regardless of the actual number of modules initially contemplated forthe bus system. Upgrading the bus system to include additional modulesrequires that a sufficient number of connectors be provided up to themaximum length (or capacity) of the channel. Typically, empty connectorsare filled with dummy modules until they are needed. Absent these spareconnectors, upgrading the bus system to include an additional modulewould require that the motherboard be replaced.

Finally, the static architecture of the conventional bus system providesa “one size fits all” approach to larger systems incorporating the bussystem. The serial arrangement of connectors and modules on amotherboard may produce an undesirably large footprint within the largersystem. Further, this configuration does not lend itself to irregular orcrowded spaces within the larger system.

BACKGROUND

The present invention provides, in certain embodiments, modules and bussystem architectures which reduce channel length and/or minimize busconnection discontinuities. Bus system architectures provided by thepresent invention may be flexibly configured according to an end user'srequirements. Numerous possibilities exist for customized bus systemconfigurations using the modules and interconnection schemes provided bythe present invention. Multiple channels may be implemented on a singlemodule and multiple modules may be connected to provide bus systemshaving relative small vertical profiles and/or horizontal footprints.The modules and/or bus system architectures may utilize various types ofconnectors, including for example finger connectors, edge connectors,and edge fingers. Any other element capable of providing an electricalconnection (e.g., contacts, pins, leads, wire bonds, solder balls, etc.)may be substituted for the connectors of the modules, bus systemsarchitectures and memory systems of the present invention. Also, asingle connector may be substituted for a plurality of connectors. Fromthe perspective of a module, a connector may allow signals to enter themodule from elsewhere and/or may allow signals to exit the module.Certain connectors are referred to herein as “ingress” or “input”connectors while certain others are referred to herein as “egress” or“output” connectors. It is understood that input connectors, ingressconnectors, output connectors and egress connectors may allow signals totravel in a first direction, a second direction or bidirectionally. Inpreferred embodiments however, a data signal sent from a memorycontroller to a memory device on a module will pass onto the modulethrough an “input” or “ingress” connector and off of the module throughan “output” or “egress” connector. Such data signal may be sampled bythe memory device after passing onto the module.

In one aspect, the present invention provides a module formed from aprinted circuit board (PCB) having primary first and second surfaces andhaving first and second ends, a plurality of integrated circuits (ICs)populating at least one of the first and second surfaces, a first set ofedge fingers disposed at the first end and on the first surface of thePCB, a second set of edge fingers disposed at the first end and on thesecond surface of the PCB, a folded bus extending from the first set ofedge fingers, substantially traversing the length of the first surface,folding back at the second end, substantially traversing the length ofthe second surface and terminating at the second set of edge fingers,and a right-angle connector mounted on either the first or secondsurface at the first end, and adapted to mechanically receive andelectrically connect another module.

In another aspect, the present invention provides a module adapted foruse in a bus system and including; a printed circuit board (PCB) havingprimary first and second surfaces, and having first and second ends, aplurality of integrated circuits (ICs) populating at least one of thefirst and second surfaces, a set of edge fingers disposed at the firstend of the PCB and on either the top or bottom surface of the PCB, aright-angle connector adapted to mechanically receive and electricallyconnect another module, the right-angle connector being mounted oneither the bottom or top surface of the PCB opposite the surface onwhich the set of edge fingers are disposed and at the second end of thePCB, and a bus extending from the set of edge fingers, substantiallytraversing the length of the module, and terminating at the right-angleconnector.

In yet another aspect, the present invention provides a module adaptedto be connected within a plurality of bus system modules, the moduleincluding a printed circuit board (PCB) having first and second primarysurfaces, first and second primary edges, and first and second ends, aplurality of integrated circuits (ICs) populating at least one of theprimary first and second surfaces, a first set of edge fingers disposedon the first primary edge between first and second ends and on the firstsurface of the PCB, a second set of edge fingers disposed on the firstprimary edge between first and second ends and on the second surface ofthe PCB, wherein the first and second set of edge fingers are adapted toconnect with an electrical connector associated with another module or amotherboard, a bus comprising a plurality of signal lines running fromat least one of the first and second set of edge fingers to a flex tapeconnector connected at the second primary edge of the PCB between thefirst and second ends, and an electrical connector connected to the flextape.

In still another aspect, the present invention provides a motherboardand a plurality of modules arranged from a first module to a lastmodule, wherein the motherboard comprises a controller and a right-angleconnector adapted to mechanically receive and electrically connect thefirst module, and wherein each one of the plurality of modules comprisesa right-angle connector adapted to receive another one of the pluralityof modules, such that, once connected via respective right-angleconnectors, the motherboard and the plurality of modules are disposed inparallel one to another.

In a further aspect, the present invention provides a module formed froma printed circuit board (PCB) having first and second primary surfacesand having a first end, a plurality of integrated circuits (ICs)populating at least one of the first and second primary surfaces, afirst and second set of input finger connectors disposed on at least oneof the first and second primary surfaces proximate to the first end, afirst and second set of output finger connectors disposed on at leastone of the first and second primary surfaces proximate to the first end,and a bus having a first channel extending from the first set of inputfinger connectors to the first set of output finger connectors andhaving a second channel extending from the second set of input fingerconnectors to the second set of output finger connectors, the busconnected to the plurality of ICs. In a preferred embodiment, the firstand second set of input finger connectors and the first and second setof output finger connectors are disposed on at least one of the firstand second primary surfaces at the first end.

In yet another aspect, the present invention provides a module includinga first printed circuit board (PCB) having first and second primarysurfaces and having a first and second ends, one or more integratedcircuits (ICs) populating at least one of the first and second primarysurfaces, a set of finger connectors disposed proximate to the first endof the first PCB and on either the first or second primary surface ofthe first PCB, a conductive interconnect electrically connected to thefirst PCB proximate to the second end of the first PCB, and a busextending from the set of finger connectors, substantially traversingthe first PCB between the first and second ends and traversing theconductive interconnect. The conductive interconnect is adapted toreceive a second PCB populated with one or more ICs. In one preferredembodiment, the module further comprises a connector connecting theconductive interconnect to the first PCB. In another preferredembodiment, the module further comprises a spacer disposed between thefirst and second PCB's. In yet another preferred embodiment, the set offinger connectors are disposed at the first end of the first PCB, thespacer is attached to the first PCB at the second end of the first PCB,and the conductive interconnect electrically connects the connector tothe first PCB at the second end of the first PCB.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a conventional bus system architecture;

FIG. 2 illustrates a module adapted for use within the presentinvention;

FIG. 3A is an edge view of one embodiment of a module according to thepresent invention;

FIGS. 3B and 3C are respectively top and bottom views of a singlechannel module according to the embodiment shown in FIG. 3A;

FIG. 3D illustrates a two channel module consistent with the embodimentshown in FIG. 3A;

FIG. 4 illustrates a bus system formed by the interconnection ofmultiple modules according to the embodiment shown in FIGS. 3A through3D;

FIG. 5A is an edge view of another embodiment of a module according tothe present invention;

FIGS. 5B and 5C are respectively top and bottom views of a singlechannel module according to the embodiment shown in FIG. 5A;

FIG. 5D illustrates a two channel module consistent with the embodimentshown in FIG. 5A;

FIG. 6 illustrates a bus system formed by the interconnection ofmultiple modules according to the embodiment shown in FIGS. 5A through5D;

FIG. 7A is an edge view of yet another embodiment of a module accordingto the present invention;

FIGS. 7B is a top view of the module of FIG. 7A further illustrating atwo channel option to the module's implementation;

FIG. 8 illustrates a bus system formed by the interconnection ofmultiple modules according to the embodiment shown in FIGS. 7A and 7B;

FIGS. 9A and 9B illustrate yet another embodiment of a single channelmodule according to the present invention;

FIG. 9C illustrates a bus system formed by the interconnection ofmultiple modules according to the embodiment shown in FIGS. 9A and 9B;

FIGS. 10A and 10B illustrate still another embodiment of a two channelmodule according to the present invention;

FIGS. 11A and 11B illustrate another embodiment of a four channel moduleaccording to the present invention;

FIGS. 11C and 11D illustrate stacked horizontal and vertical moduleconfigurations using the modules shown in FIGS. 11A and 11B;

FIG. 12A illustrates yet another one channel embodiment of the presentinvention;

FIG. 12B illustrates yet another two channel embodiment of the presentinvention;

FIG. 12C illustrates yet another four channel embodiment of the presentinvention;

FIGS. 13A, 13B, 13C, and 13D illustrate various two channel bus systemsimplemented using variations on the modules described in FIGS. 12a, 12B,and 12C;

FIGS. 14A, 14B, and 14C further illustrate various two channel bussystems having a number of different termination options; and,

FIGS. 15A and 15B illustrate embodiments using a top edge mountedflexible connector.

FIG. 16 is a perspective diagram illustrating yet another embodiment ofa two channel module in accordance with the present invention.

FIG. 17 is a perspective diagram illustrating a bus system formed by theinterconnection of multiple modules in accordance with the embodimentillustrated in FIG. 16.

FIG. 18 is a perspective diagram illustrating yet another embodiment ofa four channel module in accordance with the present invention.

FIG. 19 is a perspective diagram illustrating an embodiment of a modulewith a second printed circuit board (PCB) attached to a connector inaccordance with the present invention.

FIG. 20 is a perspective diagram illustrating the embodiment of FIG. 19with the second PCB undergoing attachment to the connector in accordancewith the present invention.

FIG. 21 is a plan view diagram illustrating an embodiment of a twochannel module in accordance with the present invention.

FIG. 22 is a plan view diagram illustrating a bus system formed by theinterconnection of multiple modules, including a module in accordancewith the embodiment illustrated in FIG. 21.

FIG. 23 is a plan view diagram illustrating a bus system formed by theinterconnection of multiple modules, including a module in accordancewith the embodiment illustrated in FIG. 21.

FIG. 24 is a plan view diagram illustrating a bus system formed by theinterconnection of multiple modules, including a module in accordancewith the embodiment illustrated in FIG. 21.

FIG. 25 is a plan view diagram illustrating a bus system formed by theinterconnection of multiple modules, including a module in accordancewith the embodiment illustrated in FIG. 21.

FIG. 26 is a plan view diagram illustrating an example of a bus systemformed by the interconnection of multiple modules, including moduleshaving multiple channels.

FIG. 27 is a plan view diagram of an example of a circuit board of a bussystem according to an embodiment of the invention.

FIG. 28 plan view diagram of an example of a circuit board of a bussystem according to an embodiment of the invention.

FIG. 29 is a plan view diagram of an embodiment of a two channel modulein accordance with the present invention.

FIG. 30 is a block diagram illustrating an example of a two-channel bussystem in accordance with an embodiment of the invention.

FIG. 31 is a block diagram illustrating an example of a four-channel bussystem in accordance with an embodiment of the invention.

FIG. 32 is a block diagram illustrating an example of a four-channel bussystem in accordance with an embodiment of the invention.

FIG. 33 is a block diagram illustrating an example of a four-channel bussystem in accordance with an embodiment of the invention.

FIG. 34 is a block diagram of an embodiment of a two-channel module inaccordance with the present invention.

FIG. 35 is a schematic diagram illustrating a technique for splitting abus into multiple paths while maintaining controlled impedance inaccordance with an embodiment of the present invention.

FIG. 36 is a schematic diagram illustrating impedances for a bus whichdoes not split into multiple paths in accordance with an embodiment ofthe present invention.

FIG. 37 is a schematic diagram illustrating impedances for a bus whichsplits into multiple paths in accordance with an embodiment of thepresent invention.

DETAILED DESCRIPTION OF THE FIGURES

The present invention can be viewed in the context of the subject matterof related and commonly assigned U.S. patent application No. 09/551,855,entitled “Multi-Slot Connector with Integrated Bus Providing ContactBetween Adjacent Modules,” filed Apr. 18, 2000, which is incorporatedherein by reference, and the subject matter of related and commonlyassigned U.S. patent application No. 09/817,828, entitled “ImprovedClock Routing in Multiple Channel Modules and Bus Systems,” filed Mar.26, 2001, which is incorporated herein by reference.

An exemplary embodiment of the module claimed in the related applicationis shown in FIG. 2. The module comprises a printed circuit board 20 anda plurality of integrated circuits (ICs) 23 a-23 f mounted thereon. Atone end of PCB 20, a first set of edge fingers 21 are disposed on afirst primary surface of the PCB and a second set of edge fingers 22 aredisposed on an opposing second primary surface of the PCB. Edge fingersare a well known connection mechanism which allow the module to bemechanically secured within a connector (not shown) and electricallyconnected to a plurality of signal lines provided at the connector. Asused herein, the phrase “disposed on” is understood to include locationson, under, and over the relevant surface or surfaces. Thus, for example,connectors, which may be described as finger connectors or edge fingers,located near an end would fall within the scope of connectors disposedon at least one of first and second primary surfaces proximate to thatend. The phrase “printed circuit board” or the word “motherboard” isunderstood to include any type of dielectric body that may supportconductors. In preferred embodiments, the dielectric body is comprisedof an epoxy, a fiberglass, a ceramic, or a polyimide, and may be rigidor flexible. In more preferred embodiments, the dielectric body iscomprised of a fiberglass. In particularly preferred embodiments, thedielectric body is comprised of FR4, FR5 or BT resin.

A bus 25 internal to the module extends from the first set of edgefingers 21, traverses substantially the entire first primary surface ofthe PCB, folds back at the distant end of the PCB, traversessubstantially the entire second primary surface of the PCB, andterminates at the second set of edge fingers 22. Bus 25 typicallycomprises a plurality of signal lines. The signal lines forming bus 25may run on top the first and second surfaces of PCB 20. Alternatively,bus 25 may be formed within the body of PCB 20. ICs 23 a-23 f arerespectively connected to this plurality of signal lines.

As described in the related application, the foregoing module may beused in conjunction with a related connector to implement bus systemshaving improved signal transmission characteristics. Overall channellength and impedance discontinuities related to motherboard connectionsare reduced. Further, by means of the novel connector and associatedmodule structure described in the related application, bus systems maybe implemented in a number of ways. For example, modules may bevertically stacked one above the other, or horizontally racked one nexttop the other within a single connector.

The present invention allows additional flexibility in the design andimplementation of bus systems. Whereas the former invention reliessubstantially upon the design of the multi-slot connector to flexiblyimplement bus systems, the present invention relies more on moduledesign.

To this end, consider the module shown in FIG. 3A. Like the module shownin FIG. 2, the module of FIG. 3A comprises a printed circuit board 30and a plurality of integrated circuits (ICs), here 23 a-23 d. Of note,the exemplary module of FIG. 2 mounts six (6) ICs connected to bus 25which is formed within the body of PCB 20, whereas the example shown inFIG. 3A mounts only four (4) ICs connected to bus 25 running on top ofthe first and second primary surfaces of PCB 30. Within the context ofthe present invention, any reasonable number of ICs may be mounted onthe module. ICs may populate one or both primary surfaces of the module.However, it is presently preferred to populate both primary surfaces ofthe module since this tends to further reduce channel length.

The module shown in FIG. 3A further comprises a right angle connector32. Right angle connector 32 is mounted on PCB 30 and comprises aconnection slot 33 adapted to receive another module. The “right-angle”nature of the connector nominally provides that slot 33 opens at a rightangle to the surface upon which it is mounted. Such an arrangementallows modules to connected one to another in parallel planes. However,one or more modules might be configured with a multi-slot connector asdescribed in the related application.

In the illustrated example of FIG. 3A, bus 25 extends from a first setof edge fingers 21 at a first end of PCB 30, substantially traverses thefirst primary surface 34, folds back at a second end of PCB 30,substantially traverses the second primary surface 35, and terminates atright angle connector 32. Thus, whereas the module bus portion shown inFIG. 2 extends from first edge fingers 21 to second set of edge fingers22, the module bus portion shown in FIG. 3 extends from first set ofedge fingers 21 to right angle connector 32. ICs 23 a-23 d respectivelyconnect to the signal lines forming bus 25.

Right angle connector 32 may include one or more signal lines 36connected back to edge fingers 21, and/or connected to a second set ofedge fingers 22. Signal lines 36 might be used, for example, as groundconnections.

Modules according to the present invention may implement one or morechannels. The term “channel” is broadly defined to include one or moresignal lines providing electrical continuity and capable ofcommunicating information between two points. A signal line may becomprised of, for example, an electrically conductive trace or wire.Preferably, a channel provides a direct metallic connection betweencomponents coupled to the channel. In the following examples, one ormore ICs are typically associated with a channel, and the channelcommunicates information from a master (a controlling device) to a slave(a responding device). However, one of ordinary skill in the art willunderstand that the ICs in the following examples may be replaced withconnectors allowing connection of an auxiliary channel. The ICs in thefollowing examples may be memory devices, receivers, transceivers, logicdevices, or other control devices. FIGS. 3B and 3C shown top and bottomviews of module illustrated in FIG. 3A.

FIG. 3D illustrates a module similar to the one illustrated in FIGS.3A-3C. However, the module shown in FIG. 3D implements two channels 37and 38 on a single module. First channel 37 is associated with a firstbus running from a first plurality of edge fingers 21 a. Second channel37 is associated with a second bus running from a second plurality ofedge fingers 21 b.

Whether the modules of the present invention implement one or morechannels, they may be flexibly configured to form a bus system. FIG. 4illustrates one such bus system. For clarity, FIG. 4 and subsequentillustrations of modules and bus systems omit labeling readilydiscernable elements such as the ICs and the PCB which have beendescribed above.

In FIG. 4, a motherboard 40 comprises a first right angle connector 50.The “motherboard” is nominally any printed circuit board having thefirst right angle connector, but typically comprises a mastercontrolling signal transmissions on the bus. In the example, a firstmodule 41 a comprising right angle connector 51 a is mechanicallysecured and electrically connected to motherboard 40 through right angleconnector 50. Similarly, right angle connector 51 a connects module 41b, and right angle connector 51 b connects module 41 c.

Such module-to-module connection may continue until a bus system ofdesired size and configuration is completed. Alternatively, at somepoint, the channel(s) defined between the master on motherboard 40 andthe ICs on the last module will reach its maximum practical length. Ineither event, when the bus system is complete the signal lines of thebus are preferably terminated in a matched impedance. Signal linetermination may be done in a set of termination resistors on the lastmodule, or by means of a special termination module 42 connected to theright angle connector 51 c of the last module. By using terminationmodule 42, the other modules need not include termination resistors.

Another embodiment of the modules according to the present invention isshown in FIGS. 5A-5D. The module shown in FIG. 5A does not make use ofthe folded bus structure described above. Rather, one or more sets offinger connectors (53 a and 53 b) are disposed on either the first orsecond primary surfaces of the module PCB. Alternatively, the first andsecond primary surfaces may each include one or more sets of edgefingers. The one or more bus(es) associated with these edge fingerssubstantially traverse the length of the module from one (1^(st)) end toanother (2^(nd)) end connecting related ICs along the way. The one ormore bus(es) then terminate at right angle connector 52.

FIGS. 5B and 5C shown respectively top and bottom views of the moduleshown in FIG. 5A. FIG. 5D illustrates a two channel version of thismodule.

An exemplary bus system configured with the modules of FIGS. 5A-5D isshown in FIG. 6. When used to configure a horizontally disposed bussystem, the bus system of FIG. 6 may provide additional mechanicalstability over the bus system illustrated in FIG. 4, since right angleconnectors will be placed on both left and right “ends” of the bussystem.

In the example shown in FIG. 6, the right angle connector on motherboard60 receives first module 61a which receives second module 61b. Module 62is a base module incorporating termination impedance 63.

Yet another embodiment of the modules according to the present inventionis shown in FIGS. 7A and 7B. This module does not use the right angleconnectors illustrated in FIGS. 4 through 6 inclusive. Rather, the oneor more bus(es) terminate at one end of the module in a flex tapeconnector 70 coupled to an electrical connector 72. Electrical connector72 may be of conventional implementation. As before, one or more sets ofedge fingers (21 and 22) are disposed at the other end of the module onthe first primary surface and/or the second primary surface of the PCB.While the embodiment shown in FIG. 7A lends itself to the same channelstructures shown in FIGS. 5B-5D, a further refinement of the channelstructures is illustrated in FIG. 7B.

In FIG. 7B, a first sub-plurality of ICs 77 populate the first primarysurface 71 of the PCB and a second sub-plurality of ICs 78 populate thesecond primary surface 73 of the PCB. A first bus originates at one setof edge fingers 21, laterally traverses the first plurality of ICs 77and terminates at flex tape connector 70. A second bus originates atanother set of edge fingers 22, laterally traverses the second pluralityof ICs 78 and terminates at flex tape connector 70. In this manner, twochannels are implemented which traverse opposing primary surfaces of thePCB in opposite directions. The width of the PCB can therefore bereduced, Compare the width of the module in FIG. 5D.

An exemplary memory system configured with the module of FIG. 7A isshown in FIG. 8. Within this system motherboard 80 comprises connector83 which receives first module 81 a which in turn receives second module81 b in connector 84 a. Connector 84 b on second module 81 b receives abase module 82 incorporating termination resistor 85. The combination offlex tape and connector allows a bus system comprising multiple modulesto be implemented in a variety of forms.

In fact, single channel and multiple channel modules may be implementedin a number forms using conventional electrical connectors. FIGS. 9A and9B illustrate a single channel module which may be “stacked” orotherwise combined with similar modules to form a bus system having areduced footprint and a relatively short channel length. Within themodule shown in FIGS. 9A and 9B, the bus runs from a first connector 90mounted on a first primary surface of the module, across the length ofthe module, and terminates in second connector 91 mounted on the secondprimary surface of the module.

FIG. 9C illustrates a bus system implemented with a number of thesemodules. A channel path 92 is indicated through the bus system whichenters the first module at its first connector and thereafter zig-zagsthough the connected modules as shown until it reaches terminationresistor 93. The modules used in the bus system of claim 9C are shownwith a single bus traversing ICs populating only one primary surface ofeach respective PCB. As noted above, a plurality of buses may occupy thechannel and one or more of the modules may include ICs on both primarysurfaces.

An exemplary two channel module is illustrated in FIGS. 10A and 10B.Here, a first channel path extends from a first connector 100 on thefirst primary surface of the PCB across the length of the PCB to asecond connector 101 on the second primary surface of the PCB. A secondchannel path extends from a third connector 102 on the first primarysurface of the PCB across the length of the PCB to a fourth connector103 on the second primary surface of the PCB. Thus, first and secondchannels run counter-directional to one another.

The module of shown in FIGS. 10A and 103B includes a single row of ICs.One of ordinary skill in the art will appreciate that a number of ICrows might be mounted on the module.

An exemplary four channel module is illustrated in FIGS. 11A and 11B.The module includes four sets of (area array) connectors 111, 112, 113,and 114, each set having a first connector mounted on the first primarysurface and a second connector mounted on the second primary surface ofthe PCB. As shown in FIG. 11B, a bus is formed between the first andsecond connector in each connector set. That is, each bus originates ata first edge of the PCB at a first connector, traverses the width of themodule, folds back at a second edge of the PCB, and retraverses thewidth of the module until it reaches the second connector in theconnector set. The modules shown in FIGS. 11A and 11B may be stacked inhorizontal 115 and vertical 116 configurations on motherboard 10 asillustrated in FIGS. 11C and 11D. The vertically stacked configuration116 of FIG. 11D is connected through a flexible connector 114.

Each one of the foregoing examples makes use of a number of connectors.In addition to providing a connection path between respective buses, thestructure of the connector may also be used to provides mechanicalsupport for modules which are stacked one above the other, or racked onenext to the other in a bus system. While this feature is often desirablein the implementation of certain bus system architectures, the presentinvention has broader applications.

For example, the present invention may be adapted to take full advantageof conventional ribbon connectors and similar flexible connectors. Bymeans of these connectors, modules forming a bus system need not bestacked or racked in close proximity one to another. Rather, module maybe placed at greater distances one to another and may be mounted withina larger system at odd angles one to another. While separating moduleswill increase the channel length, there are many applications wherereduced channel length will be happily traded away for ease andflexibility of implementation.

Before illustrating the use of flexible connectors, several modulesstructures will be described. Each of these module structures makes useof “finger connectors.” The term “set of edge fingers” has been usedabove to described a class of electrical connectors characterized by anumber of parallel electrical contacts disposed near the edge of a PCBand adapted to “mate” with a corresponding connector slot. Edge fingersare generally pushed into the connector slot to make electrical busconnections and provide mechanical support to the module.

While often located near or at the edge of a PCB, a set of fingerconnectors need not be located on the edge of the PCB. A set of fingerconnectors, like a set of edge fingers, typically comprises a set ofparallel electrical contacts. In the context of a bus, each electricalcontact typically corresponds to a bus signal line. Ribbon connectorsand other flexible parallel connectors are well adapted to interconnectsuch parallel electrical contact structures. However, a ribbon connectormay be coupled to a set of finger connectors anywhere on the PCB, notjust the edge. Thus, the term finger connector may denote an edgefinger, but may also denote a more generic electrical contact.

FIGS. 12A, 12B, and 12C illustrate a single channel module, a twochannel module, and a four channel module respectively. The singlechannel module shown in FIG. 12A comprises a set of input fingerconnectors 120 and a set of output finger connectors 121. A bussubstantially traverses the length of the module running from the set ofinput finger connectors 120 to the set of output finger connectors 121.Along the way, a plurality of ICs are connected to the bus. Themulti-channel modules shown in FIGS. 12B and 12C includes additionalsets of input finger connections and additional sets of output fingerconnectors. The third and fourth buses on the module shown in FIG. 12Care disposed the other primary surface (i.e., the bottom surface inrelation to the illustration).

In these examples, the respective sets of input finger connectors (120and 120 a-120 d) as well as the output connector 121 in FIG. 12A areedge fingers. Accordingly, the modules may be coupled within a bussystem by pushing the edge fingers into a corresponding connector(s).The corresponding connector(s) provide the input signals to the module'sbus(es). However, the sets of output finger connectors (121 a-121 d) onthe modules shown in FIGS. 12B and 12C are adapted to be connected withone or more ribbon or similar flexible connector(s).

Utilizing one or more of the modules illustrated above, bus systemshaving various configurations may be implemented using one or moreflexible connector(s). Consider the examples shown in FIGS. 13A, 13B,13C, and 13D. Only two channel bus systems are illustrated, but fromthese examples one of ordinary skill in the art will readily discern howany reasonable number of “N” channels may be implemented in a bussystem. Note that the various channels may be terminated in either a setof output finger connectors (FIGS. 13A and 13C), and/or in an on-moduleset of termination resistors (FIGS. 13B and 13D).

FIGS. 14A, 14B, and 14C illustrate further examples of two channels bussystems having various connection and termination schemes. Like the ICson these modules, more than one termination element may be mounted oneither primary surface. See termination elements 140 and 141 in FIGS.14B and 14C.

In FIGS. 15A and 15B, a flexible connector 154 is used to connectmodules. However, unlike the former examples in which a flexibleconnector was attached to the modules via a lateral edge, the bussystems shown in FIGS. 15A and 15B use a flexible connector attached viaa top edge. In particular, adjacent modules 152 a and 152 b arerespectively mounted on motherboard 159 via connectors 151 a and 151 b.Module 152 a comprises ICs 153 a and 153 b arranged in a verticalcolumn. Module 152 b comprises ICS 153 c and 153 d which are likewisearranged in a column.

In one further embodiment of the present invention, ICs 153 a, 153 b,153 c, and 153 d are connected in a channel extending from a edge lowerfingers on module 152 a, through a bus portion on module 152 a, throughflexible connector 154, down through a bus portion on module 152 b, tobe terminated at a lower set of edge fingers on module 152 b. Otherchannels may be similarly implemented.

The bus system shown in FIG. 15B illustrates another way in which aplurality of ICs may be effectively mounted on a module in one or morechannels. Here, rather than arranging ICs in vertical columns, the ICsare arranged in rows. A single channel may begin at a centrally locatedset of edge fingers, make a right turn near the center of the module,extend laterally through the row of ICs, and then make another rightturn into flexible connector 154. This path is reversed in the adjacentmodule. In this manner, first and second pluralities of ICs (156 a 156b) may be arranged in rows on each one of the modules and connected asshown.

FIG. 16 is a perspective diagram illustrating yet another embodiment ofa two channel module in accordance with the present invention. Module162 includes a first primary surface 1611 and a second primary surface1612, which opposes the first primary surface 1611. Module 162 also hasa first end 1613. Proximate to the first end 1613 are a first set ofinput finger connectors 167, a first set of output finger connectors168, a second set of input finger connectors 169, and a second set ofoutput finger connectors 1610. Alternatively, the first set of inputfinger connectors 167 and/or the second set of input finger connectors169 may provide ingress elsewhere on module 162. Likewise, the first setof output finger connectors 168 and the second set of output fingerconnectors 1610 may provide egress elsewhere on module 162. The firstset of input finger connectors 167, the first set of output fingerconnectors 168, the second set of input finger connectors 169, and thesecond set of output finger connectors 1610 are disposed on at least oneof the first primary surface 1611 and the second primary surface 1612.

A plurality of integrated circuits (ICs) populate at least one of thefirst primary surface 1611 and the second primary surface 1612. Theplurality of integrated circuits include ICs 163 and ICs 164. A bus iscoupled to the plurality of ICs. The bus includes a first channel 165extending from the first set of input finger connectors 167 to the firstset of output finger connectors 168. The bus also includes a secondchannel 166 extending from the second set of input finger connectors 169to the second set of output finger connectors 1610. The first channel165 is coupled to ICs 163, and the second channel 166 is coupled to ICs164. The first set of input finger connectors 167, the first set ofoutput finger connectors 168, the second set of input finger connectors169, and the second set of output finger connectors 1610 mate with amotherboard connector 161 mounted on a motherboard 160.

The first channel 165 and the second channel 166 may be implemented in avariety of configurations. For example, the first set of output fingerconnectors 168 may be disposed in a similar direction from the first setof input finger connectors 167 as the direction in which the second setof output finger connectors 1610 are disposed from the second set ofinput finger connectors 169. Consequently, the first channel 165 and thesecond channel 166 may be configured to convey signals in a generallysimilar direction across at least one of the first primary surface 1611and the second primary surface 1612.

As another example, the first set of output finger connectors 168 may bedisposed in an opposite direction from the first set of input fingerconnectors 167 of the direction in which the second set of output fingerconnectors 1610 are disposed from the second set of input fingerconnectors 169. Consequently, the first channel 165 and the secondchannel 166 may be configured to convey signals in generally oppositedirections across at least one of the first primary surface 1611 and thesecond primary surface 1612.

In one instance, the first set of input finger connectors 167 and thesecond set of input finger connectors 169 may be disposed near themiddle of first end 1613, with the first set of output finger connectors168 and the second set of output finger connectors 1610 disposedopposite one another along the periphery of first end 1613. In anotherinstance, the first set of input finger connectors 167 and the secondset of input finger connectors 169 may be disposed opposite one anotheralong the periphery of first end 1613, with the first set of outputfinger connectors 168 and the second set of output finger connectors1610 disposed near the middle of first end 1613. As noted previously,other locations and/or orientations of the connectors and the channelsmay be implemented.

By providing multiple channels, simultaneous independent accesses may bemade to the plurality of ICs. For example, while a first element on themotherboard 160 is communicating with ICs 163 through first channel 165,a second element on the motherboard 160 may be communicatingindependently with ICs 164 through second channel 166. Thus, theeffective bandwidth, or amount of information that may be transferredper unit time, of the bus is effectively increased through the use ofmultiple channels.

FIG. 17 is a perspective diagram illustrating a bus system formed by theinterconnection of multiple modules in accordance with the embodimentillustrated in FIG. 16. The bus system includes motherboard 170,motherboard connectors 171 a, 171 b, 171 c, and 171 d, and modules 172a, 172 b, 172 c, and 172 d. Module 172 a is coupled to motherboard 170via motherboard connector 171 a. Module 172 b is coupled to motherboard170 via motherboard connector 171 b. Module 172 c is coupled tomotherboard 170 via motherboard connector 171 c. Module 172 d is coupledto motherboard 170 via motherboard connector 171 d.

Module 172 a has a first primary surface 1711 a, a second primarysurface 1712 a, and a first end 1713 a. ICs 173 a and ICs 174 a populateat least one of the first primary surface 1711 a and the second primarysurface 1712 a. Module 172 b has a first primary surface 1711 b, asecond primary surface 1712 b, and a first end 1713 b. ICs 173 b and ICs174 b populate at least one of the first primary surface 1711 b and thesecond primary surface 1712 b. Module 172 c has a first primary surface1711 c, a second primary surface 1712 c, and a first end 1713 c. ICs 173c and ICs 174 c populate at least one of the first primary surface 1711c and the second primary surface 1712 c. Module 172 d has a firstprimary surface 1711 d, a second primary surface 1712 d, and a first end1713 d. ICs 173 d and ICs 174 d populate at least one of the firstprimary surface 1711 d and the second primary surface 1712 d.

Motherboard 170 includes a bus coupled to motherboard connector 171 a.The bus includes first channel 1714 and second channel 1715. The firstchannel 1714 is coupled through motherboard connector 171 a and thefirst set of input finger connectors 177 a to the first channel 175 athe bus of module 172 a. The first channel 175 a of the bus of module172 a is coupled through the first set of output finger connectors 178 aand through motherboard connector 171 a to a bus segment on motherboard170. The bus segment is coupled through motherboard connector 171 b tothe first channel 175 b of the bus of module 172 b. The first channel175 b of the bus of module 172 b is coupled through output fingerconnectors 178 b and through motherboard connector 171 b to another bussegment of motherboard 170. This bus segment is coupled throughmotherboard connector 171 c and through input finger connectors 177 c tothe first channel 175 c of the bus of module 172 c. The first channel175 c of the bus of module 172 c is coupled through motherboardconnector 171 c to another bus segment on motherboard 170. This bussegment is coupled through motherboard connector 171 d to the firstchannel 175 d of the bus of module 172 d. Motherboard 170 includes a buscoupled to motherboard connector 171 d. The bus includes a first channel1716 and a second channel 1717. The first channel 175 d of the bus ofmodule 172 d is coupled through output finger connectors 178 d andthrough motherboard connector 171 d to the first channel 1716 of the buson motherboard 170.

The first channel 1716 of the bus on motherboard 170 may continue toadditional circuitry on motherboard 170 or, optionally, may beterminated using bus termination 1718. Bus termination 1718 provides animpedance to match the characteristic impedance of the first channel1716 of the bus and is coupled to a termination voltage VTERM. A bustermination may include any impedance element terminating a bus.Examples of bus terminations include, but are not limited to, passivebus terminations utilizing resistive elements, active bus terminationsutilizing semiconductor devices, conductive stubs, etc. Preferred busterminations include passive bus terminations utilizing resistiveelements and active bus terminations utilizing semiconductor devices.The terms bus termination, termination, and terminator may be usedinterchangeably.

The second channel 1715 of the bus on motherboard 170 coupled tomotherboard connector 171 a is coupled to the second set of input fingerconnectors 179 a to the second channel 176 a of the bus of module 172 a.The second channel 176 a of the bus of module 172 a is coupled throughthe second set of output finger connectors 1710 a and throughmotherboard connector 171 a to a bus segment on motherboard 170. The bussegment is coupled through motherboard connector 171 b to the secondchannel 176 b of the bus of module 172 b. The second channel 176 b ofthe bus of module 172 b is coupled through motherboard connector 171 bto another bus segment of motherboard 170. This bus segment is coupledthrough motherboard connector 171 c to the second channel 176 c of thebus of module 172 c. The second channel 176 c of the bus of module 172 cis coupled through motherboard connector 171 c to another bus segment onmotherboard 170. This bus segment is coupled through motherboardconnector 171 d to the second channel 176 d of the bus of module 172 d.The second channel 176 d of the bus of module 172 d is coupled throughmotherboard connector 171 d to the second channel 1717 of the bus onmotherboard 170.

The second channel 1717 of the bus of motherboard 170 may continue toadditional circuitry on motherboard 170 or, optionally, may beterminated using bus termination 1719. Bus termination 1719 provides animpedance to match the characteristic impedance of the second channel1717 of the bus and is coupled to a termination voltage VTERM.

The bus system may be implemented in a variety of configurations. Forexample, modules 172 a, 172 b, 172 c, and 172 d may be implementedaccording to any of the configurations of the module 162 described inreference to FIG. 16, including various combinations of differentconfigurations among the modules. First and second channels of themodules may be configured to pass signals in similar or differentdirections, either within each module or between modules. For example,module 172 a may be configured to pass signals for the first channel inthe same direction as signals for the second channel, and module 172 bmay be configured to pass signals for the first channel in the samedirection as signals for the second channel, but in an oppositedirection of module 172 a. As another example, module 172 a may beconfigured to pass signals for the first channel and the second channelin opposite directions within module 172 a, but with module 172 bpassing signals for the first channel in a direction opposite that ofthe first channel of module 172 a and passing signals for the secondchannel in a direction opposite that of the second channel of module 172a. Other variations of the same or different directions within orbetween modules may be implemented.

FIG. 18 is a perspective diagram illustrating yet another embodiment ofa four channel module in accordance with the present invention. As notedabove in reference to FIG. 16, providing multiple channels allowsmultiple simultaneous independent accesses to be made to the ICs withina module, thereby increasing the effective bandwidth of the bus of amodule. As the number of channels is increased, the effective bandwidthis also increased. While various numbers of channels may be provided,FIG. 18 illustrates, as an example, a module providing four channels.

Given that module 182 has a first primary surface 1811 and a secondprimary surface 1812, each of which can accommodate integrated circuits(ICs), it is beneficial to populate both first primary surface 1811 andsecond primary surface 1812 with ICs. For example, ICs 183 and ICs 184populate the first primary surface 1811, while ICs 1814 and ICs 1815populate the second primary surface 1812. The bus of module 182 includesa first channel 185, a second channel 186, a third channel 1816, and afourth channel 1817. The first channel 185 is coupled to ICs 183. Thesecond channel 186 is coupled to ICs 184. The third channel 1816 iscoupled to ICs 1814. The fourth channel 1817 is coupled to ICs 1815.

Module 182 is removably coupled at its first end 1813 to motherboardconnector 181, which is coupled to motherboard 180. Motherboard 180conducts signals for the first channel 185 of the bus of module 182through motherboard connector 181 to a first set of input fingerconnectors 187 of module 182 and signals for the second channel 186 ofthe bus of module 182 through motherboard connector 181 to a second setof input finger connectors 189 of module 182. Motherboard 180 conductssignals for the third channel 1816 of the bus of module 182 throughmotherboard connector 181 to a third set of input finger connectors 1818of module 182 nd signals for the fourth channel 1817 of module 182through motherboard connector 181 to a fourth set of input fingerconnectors 1820 of module 182.

The first channel 185 of the bus of module 182 is coupled through thefirst set of output finger connectors 188 and through motherboardconnector 181 to motherboard 180. The second channel 186 of the bus ofmodule 182 is coupled through the second set of output finger connectors1810 and through motherboard connector 181 to motherboard 180. The thirdchannel 1816 of the bus of module 182 is coupled through the third setof output finger connectors 1819 and through motherboard connector 181to motherboard 180. The fourth channel 1817 of the bus of module 182 iscoupled through the fourth set of output finger connectors 1821 andthrough motherboard connector 181 to motherboard 180.

FIG. 19 is a perspective diagram illustrating an embodiment of a modulewith a second printed circuit board (PCB) attached to a connector inaccordance with the present invention. The module is formed from PCB192, which has a first primary surface 1911 and a second primary surface1912. PCB 192 has a first end 1913 and a second end 1914. A set offinger connectors is disposed on at least one of the first primarysurface 1911 and the second primary surface 1912 proximate to the firstend 1913 of PCB 192. The set of finger connectors are removably coupledto motherboard connector 191, which is mounted on motherboard 190.

A plurality of integrated circuits (ICs) populate at least one of thefirst primary surface 1911 and the second primary surface 1912 of PCB192. The plurality of ICs include ICs 193 and ICs 194. A conductiveinterconnect 195 is connected proximate to the second end 1914 of PCB192. A conductive interconnect 195 may include anything that provides anelectrical connection. Examples of conductive interconnects 195 include,but are not limited to, flexible cables, flex circuits, and conductiveelastomeric interconnects. A bus extends from the set of fingerconnectors, substantially traversing PCB 192 between the first end 1913and the second end 1914. The bus further traverses the conductiveinterconnect 195 so as to couple the bus to a connector 197 that iscoupled to the conductive interconnect 195. As an alternative, theconductive interconnect 195 may be connected elsewhere on PCB 192, andthe bus may be routed elsewhere on PCB 192.

The connector 197 is adapted to receive a second PCB 198 populated withat least one IC, which may include ICs 199 and ICs 1910. The second PCBhas a first primary surface 1917 and a second primary surface 1918. Thesecond PCB 198 has a first end 1919 and a second end 1920. The secondPCB 198 includes a second bus that couples the connector 197 to at leastone of the ICs 199 or ICs 1910. The second bus extends beyond the ICsand is terminated with a bus termination, such as bus termination 1915and/or bus termination 1916.

A spacer 196 is attached to one of the first primary surface 1911 of thePCB 192 or the second primary surface 1912 of the PCB 192 proximate tothe second end 1914 of PCB 192. The spacer 196 is adapted to maintain aspace between the connector 197 and the PCB 192. The space is sufficientto maintain clearance between PCB 192 and any ICs that may populate thefirst primary surface 1911 of the PCB 192 and the second PCB 198 and anyICs that may populate the second primary surface 1918 of the second PCB198. For example, while any desired amount of space may be provided, thespace may be in the range of zero to ten millimeters.

The connector 197 is preferably oriented to maintain the second PCB 198substantially parallel to the PCB 192. To maintain second PCB 198 inengagement with connector 197 at the first end 1919 of the second PCB198 and to allow its removal from connector 197, connector 197 may beprovided with latches 1921. Latches 1921 may be manipulated to removethe second PCB 198 from engagement with connector 197.

The embodiment of FIG. 19 may be practiced with multiple channels toallow multiple simultaneous independent accesses to be made to ICs 193,194, 199, and 1910. For example, the bus may comprise a first channeland a second channel. The set of finger connectors that engagemotherboard connector 191 may include a first set of finger connectorsand a second set of finger connectors, with the first channel coupled tothe first set of finger connectors and the second channel coupled to thesecond set of finger connectors. The first channel may be coupled to ICs193, while the second channel may be coupled to ICs 194. Likewise, thefirst channel and the second channel may be coupled to the second PCB198 via conductive interconnect 195 and connector 197. On the second PCB198, ICs 199 may be coupled to the first channel, while ICs 1910 may becoupled to the second channel. The first channel of the second bus ofthe second PCB 198 may terminate at bus termination 1915, while thesecond channel of the second bus of the second PCB 198 may terminate atbus termination 1916. Thus, the benefits of providing multiple channelsmay be extended from PCB 192 to include the second PCB 198.

FIG. 20 is a perspective diagram illustrating the embodiment of FIG. 19with the second PCB undergoing attachment to the connector in accordancewith the present invention. As can be seen, the second PCB 198 isoriented at an angle relative to PCB 192 rather than being parallel toPCB 192. Depending on the particular type of connector 197 used, thefirst end 1919 of second PCB 198 may be engaged in connector 197, andsecond PCB 198 may be rotated about the first end 1919 until the secondPCB 198 is engaged by latches 1921. Alternatively, other types ofconnectors 197 may be used that provide for translational motion ratherthan, or in addition to, rotational motion during engagement and/ordisengagement.

Referring to FIG. 19 and FIG. 20, the second PCB 198 may be implementedso as to be receivable in motherboard connector 191. Thus, the secondPCB 198 may be installed in motherboard connector 191 without PCB 192.The configuration may be upgraded by removing the second PCB 198 frommotherboard connector 191, inserting the second PCB 198 into connector197, and inserting PCB 192 into motherboard connector 191. Since bustermination 1915 and bus termination 1916 are provided on the second PCB198, proper bus termination is provided regardless of whether the secondPCB 198 is inserted into motherboard connector 191 or the second PCB 198is inserted into connector 197 and PCB 192 is inserted into motherboardconnector 191.

Without such an implementation, a PCB lacking ICs 199 and 1910 buthaving bus terminations 1915 and 1916 would be installed in connector197 if the use of PCB 192 without second PCB 198 is desired. However, byinstalling the second PCB 198 directly in motherboard connector 191(without PCB 192), the use of a separate PCB merely to provide properbus termination can be avoided. By relying on bus termination 1915 andbus termination 1916 to maintain proper termination impedance, theinstallation in connector 197 of a PCB containing bus termination 1915and bus termination 1916 but without ICs 199 and 1910 is renderedunnecessary.

FIG. 21 is a plan view diagram illustrating an embodiment of a twochannel module in accordance with the present invention. The module 2101includes a first channel 2102 and a second channel 2103.

First channel signals 2112 are provided to first channel 2102 via firstchannel connector 2104. First channel 2102 couples first channelconnector 2104, memory device 2106, memory device 2108, and terminator2110.

Second channel signals 2113 are provided to second channel 2103 viasecond channel connector 2105. Second channel 2103 couples secondchannel connector 2105, memory device 2107, memory device 2109, andterminator 2111.

FIG. 22 is a plan view diagram illustrating a bus system formed by theinterconnection of multiple modules, including a module in accordancewith the embodiment illustrated in FIG. 21. The bus system includesfirst module 2214, second module 2220, and third module 2201.

First channel signals 2226 are provided to first channel 2215 of firstmodule 2214. First channel 2215 of first module 2214 couples memorydevices 2216, 2217, 2218, and 2219 of first module 2214. First channel2215 of first module 2214 is coupled to first channel 2203 of thirdmodule 2201 via interconnection 2213.

Second channel signals 2227 are provided to second channel 2221 ofsecond module 2220. Second channel 2221 of second module 2220 couplesmemory devices 2222, 2223, 2224, and 2225 of second module 2220. Secondchannel 2221 of second module 2220 is coupled to second channel 2202 ofthird module 2201 via interconnection 2212.

Within third module 2201, first channel 2203 couples memory devices 2207and 2209 and terminates at terminator 2211. Second channel 2202 couplesmemory devices 2206 and 2208 and terminates at terminator 2210.

The bus system of FIG. 22 provides a useful feature in that the bussystem may be configured with only third module 2201, omitting firstmodule 2214 and second module 2220. In such a configuration, firstchannel signals 2226 may be applied to either first channel 2203 orsecond channel 2202 of third module 2201, and second channel signals2227 may be applied to whichever first channel 2203 and second channel2202 does not have first channel signals 2226 applied to it. The firstchannel signals 2226 and the second channel signals 2227 may be applied,for example, by way of circuit board conductors coupled to the thirdmodule 2201 or, for example, by using “filler” modules in place of firstmodule 2214 and second module 2220. The “filler” modules need notcontain memory devices, but provide electrical conductors to implementchannels between ingress connectors and egress connectors, therebyallowing channel signals to pass through to third module 2201.

The bus system of FIG. 22 also allows additional modules to be added,thereby enabling expansion of the bus system. For example, additionalmodules similar to first module 2214 or second module 2220 may be added.Such additional modules may, for example, be interposed between firstmodule 2214 and third module 2201 and/or between second module 2220 andthird module 2201. If additional connector slots are provided to receivesuch additional modules and the additional modules are not needed,“filler” modules may be inserted in the connector slots to providecontinuity or those connector slots may be bypassed.

FIG. 23 is a plan view diagram illustrating a bus system formed by theinterconnection of multiple modules, including a module in accordancewith the embodiment illustrated in FIG. 21. The bus system includesfirst module 2314, second module 2320, and third module 2301.

First channel signals 2326 are provided to first channel 2315 of firstmodule 2314. First channel 2315 of first module 2314 couples memorydevices 2316, 2317, 2318, and 2319 of first module 2314. First channel2315 of first module 2314 is coupled to first channel 2302 of thirdmodule 2301 via interconnection 2312.

Second channel signals 2327 are provided to second channel 2321 ofsecond module 2320. Second channel 2321 of second module 2320 couplesmemory devices 2322, 2323, 2324, and 2325 of second module 2320. Secondchannel 2321 of second module 2320 is coupled to second channel 2303 ofthird module 2301 via interconnection 2313.

Within third module 2301, first channel 2302 couples memory devices 2306and 2308 and terminates at terminator 2310. Second channel 2303 couplesmemory devices 2307 and 2309 and terminates at terminator 2311.

As described above in reference to FIG. 22, the bus system of FIG. 23 isalso expandable and may also be reduced to a bus system comprising onlythird module 2301, without first module 2314 and second module 2320.Likewise, additional modules and/or “filler” modules may be used withthe bus system of FIG. 23.

FIG. 24 is a plan view diagram illustrating a bus system formed by theinterconnection of multiple modules, including a module in accordancewith the embodiment illustrated in FIG. 21. The bus system includesfirst module 2414, second module 2420, and third module 2401.

First channel signals 2426 are provided to first channel 2415 of firstmodule 2414. First channel 2415 of first module 2414 couples memorydevices 2416, 2417, 2418, and 2419 of first module 2414. First channel2415 of first module 2414 is coupled to first channel 2403 of thirdmodule 2401 via interconnection 2413.

Second channel signals 2427 are provided to second channel 2421 ofsecond module 2420. Second channel 2421 of second module 2420 couplesmemory devices 2422, 2423, 2424, and 2425 of second module 2420. Secondchannel 2421 of second module 2420 is coupled to second channel 2402 ofthird module 2401 via interconnection 2412.

Within third module 2401, first channel 2403 couples memory devices 2407and 2409 and terminates at terminator 2411. Second channel 2402 couplesmemory devices 2406 and 2408 and terminates at terminator 2410.

As described above in reference to FIG. 22, the bus system of FIG. 24 isalso expandable and may also be reduced to a bus system comprising onlythird module 2401, without first module 2414 and second module 2420.Likewise, additional modules and/or “filler” modules may be used withthe bus system of FIG. 24.

FIG. 25 is a plan view diagram illustrating a bus system formed by theinterconnection of multiple modules, including a module in accordancewith the embodiment illustrated in FIG. 21. The bus system includes acontroller 2530, a first module 2514, a second module 2520, and a thirdmodule 2501. Controller 2530 includes a first channel 2528 and a secondchannel 2529. First channel 2528 of controller 2530 is coupled to firstchannel ingress connector 2531 of first module 2514 via interconnection2526. Second channel 2529 of controller 2530 is coupled to secondchannel ingress connector 2533 of second module 2520 via interconnection2527.

First channel ingress connector 2531 of first module 2514 is coupled tofirst channel 2515 of first module 2515. First channel 2515 couplesmemory devices 2516, 2517, 2518, and 2519 and continues to first channelegress connector 2532 of first module 2514. First channel egressconnector 2532 of first module 2514 is coupled to first channel ingressconnector 2504 of third module 2501 via interconnection 2512.

Second channel ingress connector 2527 of second module 2520 is coupledto second channel 2521 of second module 2520. Second channel 2521 ofsecond module 2520 couples memory modules 2522, 2523, 2524, and 2525 andcontinues to second channel egress connector 2534 of second module 2520.Second channel egress connector 2534 of second module 2520 is coupled tosecond channel ingress connector 2505 of third module 2501 viainterconnection 2513.

Within third module 2501, first channel ingress connector 2504 iscoupled to first channel 2502. First channel 2502 couples memory devices2506 and 2508 and continues to terminator 2510. Second channel ingressconnector 2505 of third module 2501 is coupled to second channel 2503.Second channel 2503 couples memory devices 2507 and 2509 and continuesto terminator 2511.

As described above in reference to FIG. 22, the bus system of FIG. 25 isalso expandable and may also be reduced to a bus system comprising onlythird module 2501, without first module 2514 and second module 2520.Likewise, additional modules and/or “filler” modules may be used withthe bus system of FIG. 25.

FIG. 26 is a plan view diagram illustrating an example of a bus systemformed by the interconnection of multiple modules, including moduleshaving multiple channels. The bus system includes a controller 2630, afirst module 2614, a second module 2620, and a third module 2601.Controller 2630, which may be referred to as a control circuit, providescontrol of operations within the first module 2614, the second module2620, and/or the third module 2601. Controller 2630 includes a firstchannel 2628, a second channel 2662, a third channel 2663, and a fourthchannel 2629. First channel 2628 of controller 2630 is coupled to firstchannel ingress connector 2631 of first module 2614 via interconnection2626. Second channel 2662 of controller 2630 is coupled to secondchannel ingress connector 2647 of second module 2620 via interconnection2664. Third channel 2663 of controller 2630 is coupled to third channelingress connector 2656 of second module 2620 via interconnection 2665.Fourth channel 2629 of controller 2630 is coupled to fourth channelingress connector 2633 of second module 2620 via interconnection 2627.

First channel ingress connector 2631 of first module 2614 is coupled tofirst channel 2615 of first module 2615. First channel 2615 couplesmemory devices 2616, 2617, 2618, and 2619 and continues to first channelegress connector 2632 of first module 2614. First channel egressconnector 2632 of first module 2614 is coupled to first channel ingressconnector 2604 of third module 2601 via interconnection 2612.

Second channel ingress connector 2647 of first module 2614 is coupled tosecond channel 2649 of first module 2614. Second channel 2649 of firstmodule 2614 couples memory devices 2650, 2651, 2652, and 2653 andcontinues to second channel egress connector 2648 of first module 2614.Second channel egress connector 2648 of first module 2614 is coupled tosecond channel ingress connector 2638 of third module 2601 viainterconnection 2666.

Third channel ingress connector 2656 of second module 2620 is coupled tothird channel 2657 of second module 2620. Third channel 2657 couplesmemory devices 2658, 2659, 2660, and 2661 and continues to third channelegress connector 2655 of second module 2620. Third channel egressconnector 2655 of second module 2620 is coupled to third channel ingressconnector 2639 of third module 2601 via interconnection 2667.

Fourth channel ingress connector 2633 of second module 2620 is coupledto fourth channel 2621 of second module 2620. Fourth channel 2621couples memory devices 2622, 2623, 2624, and 2625 and continues tofourth channel egress connector 2634 of second module 2620. Fourthchannel egress connector 2634 of second module 2620 is coupled to fourthchannel ingress connector 2605 of third module 2601 via interconnection2613.

Within third module 2601, first channel ingress connector 2604 iscoupled to first channel 2602. First channel 2602 couples memory devices2606 and 2608 and continues to terminator 2610. Second channel ingressconnector 2638 of third module 2601 is coupled to second channel 2636.Second channel 2636 couples memory devices 2640 and 2642 and continuesto terminator 2644. Third channel ingress connector 2639 is coupled tothird channel 2637. Third channel 2637 couples memory devices 2641 and2643 and continues to terminator 2645. Fourth channel ingress connector2605 is coupled to fourth channel 2603. Fourth channel 2603 couplesmemory devices 2607 and 2609 and continues to terminator 2611.

As described above in reference to FIG. 22, the bus system of FIG. 26 isalso expandable and may also be reduced to a bus system comprising onlythird module 2601, without first module 2614 and second module 2620.Likewise, additional modules and/or “filler” modules may be used withthe bus system of FIG. 26.

FIG. 27 is a plan view diagram of an example of a circuit board of a bussystem according to an embodiment of the invention. The circuit boardcomprises a first module slot 2701, a second module slot 2702, and athird module slot 2703. First channel signals are provided to a firstchannel ingress connector 2704 of the first module slot 2701 via firstchannel bus 2710. Second channel signals are provided to a secondchannel ingress connector 2707 of the second module slot 2702 via secondchannel bus 2711. A first channel egress connector 2705 of the firstmodule slot 2701 is coupled to a first channel ingress connector 2709 ofthe third module slot 2703 via first channel bus segment 2712. A secondchannel egress connector 2706 of the second module slot 2702 is coupledto a second channel ingress connector 2708 of the third module slot 2703via second channel bus segment 2713. Since each of the module slots areconfigured such that a space without connectors exists between theingress connector and the egress connector, one or more conductors ofone or more of the channel buses may be routed along the circuit boardbetween a module's ingress connector and that module's egress connector.Thus, more that one channel may approach the module slots from the samedirection. Alternatively, one or more conductors of one or more channelbuses may be routed around the end of an ingress or egress connector ofa module opposite that module's respective egress or ingress connector.

While separate ingress and egress connectors are identified in referenceto FIG. 27, it should be understood that the ingress and egressconnectors may be implemented as separate connectors or may be combinedinto a single connector structure accommodating a plurality ofconductors. For example, if a connector having a connector pin array isused, one set of one or more connector pins may be used to implement aningress connector and a second set of one or more connector pins may beused to implement an egress connector. Optionally, a portion of theconnector shell that would otherwise accommodate additional connectorpins may be left vacant to provide a region near the vacancies whereconductors may be routed, for example on a printed circuit board.

A plurality of the conductors of a channel bus may be configured to beof equal length. Thus, signals introduced at one end of those conductorsof the channel bus will arrive at the opposite end of those conductorsat the same time. Even if topological constraints cause some conductorsto be longer than others, additional length may be introduced into theshorter conductors, for example by using a zig-zag or switchback routingpattern, to compensate and cause all conductors to have the same length.

The circuit board of FIG. 27 may be practiced as a motherboard, withfirst channel ingress connector 2704, first channel egress connector2705, second channel egress connector 2706, second channel ingressconnector 2707, second channel ingress connector 2708, and first channelingress connector 2709 practiced as motherboard connectors. Also, acontroller or control circuit such as controller 2630 of FIG. 26 may becoupled to first channel bus 2710 and/or second channel bus 2711.

FIG. 28 plan view diagram of an example of a circuit board of a bussystem according to an embodiment of the invention. This example of acircuit board shares the configuration illustrated in FIG. 28 andincludes illustration of channel coupling internal to modules andtermination of channels within a module. The circuit board comprises afirst module slot 2801, a second module slot 2802, and a third moduleslot 2803. First channel signals are provided to a first channel ingressconnector 2804 of the first module slot 2801 via a first conductor 2810of a first channel bus. Second channel signals are provided to a secondchannel ingress connector 2807 of the second module slot 2802 via afirst conductor 2811 of a second channel bus. The first conductor 2810of the first channel bus is coupled to a first conductor 2812 of a firstchannel bus segment at first channel egress connector 2805 via a firstconductor 2816 of a channel of a first module coupled to the firstchannel ingress connector 2804 and to the first channel egress connector2805. The first channel egress connector 2805 of the first module slot2801 is coupled to a first channel ingress connector 2809 of the thirdmodule slot 2803 via a first conductor 2812 of the first channel bussegment.

The first conductor 2811 of the second channel bus is coupled to a firstconductor 2813 of a second channel bus segment at second channel egressconnector 2806 via a first conductor 2817 of a channel of a secondmodule coupled to the second channel ingress connector 2802 and thesecond channel egress connector 2806. The second channel egressconnector 2806 of the second module slot 2802 is coupled to a secondchannel ingress connector 2808 of the third module slot 2803 via thefirst conductor 2813 of the second channel bus segment.

Within a third module coupled to first channel ingress connector 2809 ofthe third module slot 2803 and to the second channel ingress connector2808 of the third module slot 2803, a first conductor 2818 of a firstchannel couples the first conductor 2812 of the first channel bussegment to a first terminator 2815. A first conductor 2819 of a secondchannel couples the first conductor 2813 of the second channel bussegment to a second terminator 2814. The first conductor 2818 of thefirst channel and the first conductor 2819 of the second channel mayalso be coupled to the same or different memory devices within the thirdmodule. While the bus system has been described with respect to a singleconductor, it can be readily appreciated that the single conductor maybe instantiated as many times as desired to provide as many conductorsas desired.

FIG. 29 is a plan view diagram of an embodiment of a two channel modulein accordance with the present invention. The module 2901 includes afirst channel ingress connector 2904, a second channel ingress connector2905, memory devices 2906, 2907, 2908, and 2909, and terminators 2910and 2911. A first channel 2902 couples the first channel ingressconnector 2904 to memory 2906 and 2908 and to terminator 2910. A secondchannel 2903 couples the second channel ingress connector 2905 to memorydevices 2907 and 2909 and to terminator 2911. The first channel 2902 andthe second channel 2903 each comprise a plurality of conductors. Thelength of each of the conductors which a channel comprises arepreferably of equal length. The length between the ingress connector andthe terminator is preferably equal among conductors of a channel. Thelength between the ingress connector and a memory device coupled to thechannel is preferably equal among conductors of the channel. Techniquessuch as those described above may be used to adjust the lengths of theconductors to assure equal length.

FIG. 30 is a block diagram illustrating an example of a two-channel bussystem in accordance with an embodiment of the invention. The bus systemcomprises a first module 3001 and a second module 3002. The first modulecomprises memory devices 3003 and 3004 and terminators 3010 and 3014.The second module comprises memory devices 3005 and 3006 and terminators3009 and 3013. A first data channel 3007 is coupled to a first ingressconnector on the first module 3001, to a first memory device 3003 on thefirst module 3001, and to a first egress connector on the first module3001. From there, the first data channel 3007 is coupled to a firstingress connector on the second module 3002, to a first memory device3005 on the second module 3002, and to a terminator 3009 on the secondmodule 3002. A second data channel 3008 is coupled to a second ingressconnector on the second module 3002, to a second memory device 3006 onthe second module 3002, and to a second egress connector on the secondmodule 3002. From there, the second data channel 3008 is coupled to asecond ingress connector on the first module 3001, to a second memorydevice 3004 on the first module 3001, and to a terminator 3010 on thefirst module 3001.

A first request channel 3012 is coupled to an ingress connector on firstmodule 3001, to memory devices 3004 and 3003 on the first module 3001,and to terminator 3014 on the first module 3001. A second requestchannel 3011 is coupled to an ingress connector on second module 3002,to memory devices 3005 and 3006 on the second module 3002, and toterminator 3013.

Since the first module 3001 and the second module 3002 have an identicalinternal configuration (although they are depicted as reversed relativeto one another in FIG. 30), a multiple module bus system may beconstructed with a minimum number-of distinct components. One or moreadditional modules comprising ingress connectors, memory devices, andegress connectors for either or both channels may be interposed betweenfirst module 3001 and second module 3002 to allow expansion of the bussystem.

As can be seen from FIG. 30, in this example, a module provides ingressand egress for one channel and ingress and termination for anotherchannel. The module passes one channel through to another module whileterminating the other channel. By using two such modules, as shown, onechannel can pass through a first module and terminate on a second modulewhile another channel can pass through the second module and terminateon the first module.

The bus system of FIG. 30 is expandable. Additional modules and/or“filler” modules may be added, for example, between first module 3001and second module 3002. Such additional modules and/or “filler” modulesneed not provide terminators for the data channels, but may receive adata channel at an ingress connector, couple the data channel to one ormore memory devices, and provide the data channel to an egressconnector. Alternatively, such modules may provide termination.Additional request channels may be provided to the additional modules,or the existing request channels may be shared with the additionalmodules, for example, through the use of one or more splitters. Asanother alternative, either of first module 3001 and second module 3002may be omitted and replace with a similar module lacking memory devices.Such a module provides continuity and termination, but saves the cost ofthe memory devices for systems in which such memory devices are notneeded.

FIG. 31 is a block diagram illustrating an example of a four-channel bussystem in accordance with an embodiment of the invention. The bus systemcomprises a first module 3101 and a second module 3102. The first modulecomprises memory devices 3103, 3115, 3104, and 3116 and terminators3110, 3122, and 3114. The second module comprises memory devices 3105,3117, 3106, and 3118 and terminators 3109, 3121, and 3113. A first datachannel 3107 is coupled to an ingress connector on the first module3101, to a memory device 3103 on the first module 3101, to a memorydevice 3115 on the first module 3101, and to an egress connector on thefirst module 3101. From there, the first data channel 3107 is coupled toan ingress connector on the second module 3102, to a memory device 3105on the second module 3102, to a memory device 3117 on the second module3102, and to a terminator 3109 on the second module 3102.

A second data channel 3119 is coupled to an ingress connector on thefirst module, to a memory device 3103 on the first module 3101, to amemory device 3115 on the first module 3101, and to an egress connectoron the first module 3101. From there, the second data channel is coupledto an ingress connector on the second module 3102, to a memory device3105 on the second module 3102, to a memory device 3117 on the secondmodule 3102, and to terminator 3121 on the second module 3102.

A third data channel 3108 is coupled to an ingress connector on thesecond module 3102, to a memory device 3106 on the second module 3102,to a memory device 3118 on the second module 3102, and to an egressconnector on the second module 3102. From there, the third data channel3108 is coupled to an ingress connector on the first module 3101, to amemory device 3104 on the first module 3101, to a memory device 3116 onthe first module 3101, and to a terminator 3110 on the first module3101.

A fourth data channel 3120 is coupled to an ingress connector on thesecond module 3102, to a memory device 3106 on the second module 3102,to a memory device 3118 on the second module 3102, and to an egressconnector on the second module 3102. From there, the fourth data channel3120 is coupled to an ingress connector on the first module 3101, to amemory device 3104 on the first module 3101, to a memory device 3116 onthe first module 3101, and to a terminator 3122 on the first module3101.

A first request channel 3112 is coupled to an ingress connector on firstmodule 3101, to memory devices 3104, 3116, 3103, and 3115 on the firstmodule 3101, and to terminator 3114 on the first module 3101. A secondrequest channel 3111 is coupled to an ingress connector on second module3102, to memory devices 3105, 3117, 3106, and 3118 on the second module3102, and to terminator 3113.

Since the first module 3101 and the second module 3102 have an identicalinternal configuration (although they are depicted as reversed relativeto one another in FIG. 31), a multiple module bus system may beconstructed with a minimum number of distinct components. One or moreadditional modules comprising ingress connectors, memory devices, andegress connectors for either or both channels may be interposed betweenfirst module 3101 and second module 3102 to allow expansion of the bussystem.

The bus system of FIG. 31 is expandable. Additional modules and/or“filler” modules may be added, for example, between first module 3101and second module 3102. Such additional modules and/or “filler” modulesneed not provide terminators for the data channels, but may receive adata channel at an ingress connector, couple the data channel to one ormore memory devices, and provide the data channel to an egressconnector. Alternatively, such modules may provide termination.Additional request channels may be provided to the additional modules,or the existing request channels may be shared with the additionalmodules, for example, through the use of one or more splitters.

It should be noted that other variations of FIG. 31 are possible. Forexample, the numbers of ingress connectors, memory devices, channels,egress connectors, and terminations may be varied.

FIG. 32 is a block diagram illustrating an example of a four-channel bussystem in accordance with an embodiment of the invention. The bus systemcomprises a first module 3201 and a second module 3202. The first modulecomprises memory devices 3203, 3215, 3204, and 3216 and terminators3210, 3222, and 3214. The second module comprises memory devices 3205,3217, 3206, and 3218 and terminators 3209, 3221, and 3213. A first datachannel 3207 is coupled to an ingress connector on the first module3201, to a memory device 3203 on the first module 3201, and to an egressconnector on the first module 3201. From there, the first data channel3207 is coupled to an ingress connector on the second module 3202, to amemory device 3205 on the second module 3202, and to a terminator 3209on the second module 3202.

A second data channel 3219 is coupled to an ingress connector on thefirst module, to a memory device 3215 on the first module 3201, and toan egress connector on the first module 3201. From there, the seconddata channel is coupled to an ingress connector on the second module3202, to a memory device 3217 on the second module 3202, and toterminator 3221 on the second module 3202.

A third data channel 3208 is coupled to an ingress connector on thesecond module 3202, to a memory device 3206 on the second module 3202,and to an egress connector on the second module 3202. From there, thethird data channel 3208 is coupled to an ingress connector on the firstmodule 3201, to a memory device 3204 on the first module 3201, and to aterminator 3210 on the first module 3201.

A fourth data channel 3220 is coupled to an ingress connector on thesecond module if 3202, to a memory device 3218 on the second module3202, and to an egress connector on the second module 3202. From there,the fourth data channel 3220 is coupled to an ingress connector on thefirst module 3201, to a memory device 3216 on the first module 3201, andto a terminator 3222 on the first module 3201.

A first request channel 3212 is coupled to an ingress connector on firstmodule 3201, to memory devices 3204, 3216, 3203, and 3215 on the firstmodule 3201, and to terminator 3214 on the first module 3201. A secondrequest channel 3211 is coupled to an ingress connector on second module3202, to memory devices 3205, 3217, 3206, and 3218 on the second module3202, and to terminator 3213.

Since the first module 3201 and the second module 3202 have an identicalinternal configuration (although they are depicted as reversed relativeto one another in FIG. 32), a multiple module bus system may beconstructed with a minimum number of distinct components. One or moreadditional modules comprising ingress connectors, memory devices, andegress connectors for either or both channels may be interposed betweenfirst module 3201 and second module 3202 to allow expansion of the bussystem.

The bus system of FIG. 32 is expandable. Additional modules and/or“filler” modules may be added, for example, between first module 3201and second module 3202. Such additional modules and/or “filler” modulesneed not provide terminators for the data channels, but may receive adata channel at an ingress connector, couple the data channel to one ormore memory devices, and provide the data channel to an egressconnector. Alternatively, such modules may provide termination.Additional request channels may be provided to the additional modules,or the existing request channels may be shared with the additionalmodules, for example, through the use of one or more splitters.

FIG. 33 is a block diagram illustrating an example of a four-channel bussystem in accordance with an embodiment of the invention. The bus systemcomprises a first module 3301 and a second module 3302. The first modulecomprises memory devices 3303, 3315, 3323, 3327, 3304, 3316, 3326, and3330 and terminators 3310, 3322, 3314, and 3333. The second modulecomprises memory devices 3305, 3317, 3325, 3329, 3306, 3318, 3324, and3328 and terminators 3309, 3321, 3313,and 3334. A first data channel3307 is coupled to an ingress connector on the first module 3301, to amemory device 3303 on the first module 3301, to a memory device 3315 onthe first module 3301, and to an egress connector on the first module3301. From there, the first data channel 3307 is coupled to an ingressconnector on the second module 3302, to a memory device 3305 on thesecond module 3302, to a memory device 3317 on the second module 3302,and to a terminator 3309 on the second module 3302.

A second data channel 3319 is coupled to an ingress connector on thefirst module, to a memory device 3323 on the first module 3301, to amemory device 3327 on the first module 3301, and to an egress connectoron the first module 3301. From there, the second data channel is coupledto an ingress connector on the second module 3302, to a memory device3325 on the second module 3302, to a memory device 3329 on the secondmodule 3302, and to terminator 3321 on the second module 3302.

A third data channel 3308 is coupled to an ingress connector on thesecond module 3302, to a memory device 3306 on the second module 3302,to a memory device 3318 on the second module 3302, and to an egressconnector on the second module 3302. From there, the third data channel3308 is coupled to an ingress connector on the first module 3301, to amemory device 3304 on the first module 3301, to a memory device 3316 onthe first module 3301, and to a terminator 3310 on the first module3301.

A fourth data channel 3320 is coupled to an ingress connector on thesecond module 3302, to a memory device 3324 on the second module 3302,to a memory device 3328 on the second module 3302, and to an egressconnector on the second module 3302. From there, the fourth data channel3320 is coupled to an ingress connector on the first module 3301, to amemory device 3326 on the first module 3301, to a memory device 3330 onthe first module 3301, and to a terminator 3322 on the first module3301.

A first request channel 3335 is coupled to an ingress connector on firstmodule 3301. The first request channel is split into a first branch 3311and a second branch 3331 using a splitter. The splitter preferablycouples the first request channel 3335 to the first branch 3311 and tothe second branch 3331 while maintaining continuity of impedance. Thefirst branch 3311 is coupled to memory devices 3304, 3316, 3303, and3315 on the first module 3301, and to terminator 3314 on the firstmodule 3301. The second branch 3331 is coupled to the memory devices3326, 3330, 3323, and 3327 on the first module 330, and to terminator3333 on the first module 3301. A second request channel 3336 is splitinto a first branch 3312 and a second branch 3332 using a splitter. Thesplitter preferably couples the second request channel 3336 to the firstbranch 3312 and to the second branch 3332 while maintaining continuityof impedance. The first branch 3312 is coupled to memory devices 3305,3317, 3306, and 3318 on the second module 3302, and to terminator 3313.The second branch 3332 is coupled to memory devices 3325, 3329, 3324,and 3328, and to terminator 3334.

The first request channel 3335 and the second request channel 3336 maybe implemented in a variety of configurations. For example, instead ofsplitting a request channel into two branches, a request channel may becoupled to all of the memory devices on a module and terminated with asingle terminator. Thus, the splitter and one terminator may beobviated. Also, a plurality of request channels may be coupled to eachmodule, with termination provided for each request channel.

Since the first module 3301 and the second module 3302 have an identicalinternal configuration (although they are depicted as reversed relativeto one another in FIG. 33), a multiple module bus system may beconstructed with a minimum number of distinct components. One or moreadditional modules comprising ingress connectors, memory devices, andegress connectors for either or both channels may be interposed betweenfirst module 3301 and second module 3302 to allow expansion of the bussystem.

The bus system of FIG. 33 is expandable. Additional modules and/or“filler” modules may be added, for example, between first module 3301and second module 3302. Such additional modules and/or “filler” modulesneed not provide terminators for the data channels, but may receive adata channel at an ingress connector, couple the data channel to one ormore memory devices, and provide the data channel to an egressconnector. Additional request channels may be provided to the additionalmodules, or the existing request channels may be shared with theadditional modules, for example, through the use of one or moresplitters.

FIG. 34 is a block diagram of an embodiment of a two-channel module inaccordance with the present invention. This embodiment provides busesthat split into multiple paths while maintaining controlled impedance.For example, while other impedances may be used, a 28 ohm bus may besplit into two 56 ohm paths, which may optionally be merged into another28 ohm bus. The two-channel module 3401 includes an RQ request bus 3402that splits into paths 3440 and 3441. Path 3440 is coupled to memorydevices 3412, 3414, 3416, and 3418, and terminates in resistor 3428coupled to ground 3429. Path 3441 is coupled to memory devices 3420,3422, 3424, and 3426, and terminates in resistor 3434 coupled to ground3435. CFM(1) clock bus 3404 splits into paths 3444 and 3445. Path 3444is coupled to memory devices 3412, 3414, 3416, and 3418 and terminatesin resistor 3430 coupled to ground 3431. Path 3445 is coupled to memorydevices 3420, 3422, 3424, and 3426 and terminates in resistor 3436coupled to ground >3437. CTM(1) clock bus 3406 splits into paths 3448and 3449. Path 3448 is coupled to memory devices 3412, 3414, 3416, and3418. Path 3449 is coupled to memory devices 3420, 3422, 3424, and 3426.Paths 3448 and 3449 are combined into bus 3452, which may exit module3401 and be coupled to other components, for example, other modules.Data signals are applied to DQ(A) data bus 3408, which enters module3401 and is coupled to memory devices 3412, 3414, 3416, and 3418 andterminates in resistor 3432 coupled to ground 3433. Data signals areapplied to DQ(B) data bus 3410, which is applied to module 3401 andcoupled to memory devices 3420, 3422, 3424, and 3426 and terminated byresistor 3438 coupled to ground 3439.

RQ request bus 3403 splits into paths 3442 and 3443. Path 3442 iscoupled to memory devices 3413, 3415, 3417, and 3419. Path 3443 iscoupled to memory devices 3421, 3423, 3425, and 3427. Paths 3442 and3443 are merged to provide bus 3453, which may exit module 3401 and, forexample, be coupled to other components such as other modules. CFM(2)clock bus 3405 enters module 3401 and splits into paths 3446 and 3447.Path 3446 is coupled to memory devices 3413, 3415, 3417, and 3419. Path3447 is coupled to memory devices 3421, 3423, 3425, and 3427. Paths 3446and 3447 are merged to form bus 3454, which may exit module 3401 and becoupled to other components, for example, other modules. CTM(2) clockbus 3407 enters module 3401 and splits into paths 3450 and 3451. Path3450 is coupled to memory devices 3413, 3415, 3417, and 3419. Path 3451is coupled to memory devices 3421, 3423, 3425, and 3427. Paths 3450 and3451 are merged to form bus 3455, which may exit module 3401 and becoupled to other components, for example, other modules. Data signalsare applied to DQ(C) data bus 3409, which enters module 3401 and iscoupled to memory devices 3413, 3415, 3417, and 3419. DQ(C) data bus3409 may also exit module 3401 and be coupled to other components, forexample, other modules. Data signals are applied to DQ(D) data bus 3411,which enters module 3401 and is coupled to memory devices 3421, 3423,3425, and 3427. DQ(D) data bus 3411 may exit module 3401 and be coupledto other components, for example, other modules.

While various bus terminations are described as resistors coupled toground, it is understood that other bus terminations may be used. Forexample, resistors may be coupled to any termination voltage, such asany DC voltage or any voltage that exhibits the properties of such a DCvoltage when used for termination of a bus. As additional examples,other types of passive terminations, active terminations, and/or stubterminations may be used. Terminations may be implemented within anintegrated circuit, separately from an integrated circuit, and, in somecases, terminations may be omitted. For example, terminations may beomitted when a bus is configured so as to prevent any reflections fromexceeding a specified amplitude or when any reflections that occur willnot impair one or more bus performance parameters, such as a data rateor an error rate, to a meaningful degree.

Thus, in accordance with an embodiment of the invention, a module may beformed from a printed circuit board (PCB). The module comprises a firstset of integrated circuits (ICs), a second set of ICs, a first inputconnector, and a first ingress bus. The first set of ICs is mounted onthe PCB. The second set of ICs is mounted on the PCB. The first inputconnector is disposed on the PCB. The first ingress bus is coupled tothe first input connector. The first ingress bus is split into a firstpath and a second path. The first path is coupled to the first set ofICs, and the second path is coupled to the second set of ICs. The firstingress bus has a first characteristic impedance, and the first path andthe second path have a combined effective impedance substantially equalto the first characteristic impedance. By being substantially equal, theimpedances prevent interference from impedance discontinuities, forexample, interference caused by reflections. Such interference iseffectively prevented if performance parameters, for example, a datarate or an error rate, are not adversely affected by the interference toa meaningful degree. In preferred embodiments, the impedances aresubstantially equal if the difference between the first characteristicimpedance and the combined effective impedance does not exceed 15%. Inmore preferred embodiments, the difference does not exceed 10%.

Optionally, the first path is coupled to a first terminator, and thesecond path is coupled to a second terminator. As another option, themodule further comprises a first output connector disposed on the PCBand a first egress bus coupled to the first output connector. The firstpath and the second path are merged into the first egress bus. The firstegress bus has a second characteristic impedance substantially equal tothe first characteristic impedance. By being substantially equal, theimpedances prevent interference from impedance discontinuities, forexample, interference caused by reflections.

FIG. 35 is a schematic diagram illustrating a technique for splitting abus into multiple paths while maintaining controlled impedance inaccordance with an embodiment of the present invention. An ingress busis represented by transmission line 3501. The ingress bus splits into aplurality of paths represented by transmission lines 3502, 3503, and3504. The plurality of paths are merged to form an egress busrepresented by transmission line 3505. Signals are applied to a firstend of transmission line 3501. A second end of transmission line 3501 iscoupled to a first end of each of transmission lines 3502, 3503, and3504 at node 3506. A second end of each of transmission lines 3502,3503, and 3504 is coupled to a first end of transmission line 3505 atnode 3507. A second end of transmission line 3505 provides an output forsignals.

Transmission lines 3501 and 3505 have a characteristic impedance of Z0.Each of transmission lines 3502, 3503, and 3504 have a characteristicimpedance N×Z0, where N equals the number of transmission lines 3502,3503, and 3504 representing the plurality of paths. The parallelcombination of the plurality of paths has an effective impedance of thecharacteristic impedance of the transmission lines representing each ofthe paths divided by the number of paths. Expressed mathematically, theeffective impedance for the parallel combination of paths is N×Z0divided by N, which equals Z0, the impedance of transmission lines 3501and 3505. By configuring the paths such that each path has acharacteristic impedance equal to the number of paths times thecharacteristic impedance of the bus to which the paths are coupled,continuity of impedance is provided and interference of impedancemismatches, such as reflection, is avoided.

For example, a signal applied to transmission line 3501 propagates tonode 3506. The signal arriving at node 3506 causes parallel signals topropagate along transmission lines 3502, 3503, and 3504. The wavesrepresenting the signal propagating along transmission lines 3502, 3503,and 3504 retain substantially the same timing relationship amongtransmission lines 3502, 3503, and 3504, arriving at node 3507substantially simultaneously. By arriving at node 3507 substantiallysimultaneously, these waves are recombined at node 3507, driving thesignal onto transmission line 3505 without detrimental levels ofreflection or attenuation. Thus, the fidelity of the signal is preservedthroughout the splitting, propagation, merging, and subsequentpropagation.

In accordance with FIG. 35, a module is provided wherein a bus includesa first channel. The first channel has a first characteristic impedanceand is coupled to a plurality of paths. The plurality of paths arecoupled to a plurality of ICs. The plurality of paths have a combinedeffective impedance substantially equal to the first characteristicimpedance.

FIG. 36 is a schematic diagram illustrating impedances for a bus whichdoes not split into multiple paths in accordance with an embodiment ofthe present invention. Driver 3601 is coupled to RACPKG device 3602.This RACPKG device may, for example, be a component of a memorycontroller or an interface for coupling a memory controller to a memorydevice. RACPKG device 3602 is coupled through a 28 ohm motherboardconductor 3603 to via 3604. Via 3604 is coupled to connector 3605.Connector 3605 is coupled to 28 ohm module conductor 3606. 28 ohm moduleconductor 3606 is coupled to connector 3607. Connector 3607 is coupledto via 3608 and 28 ohm motherboard conductor 3609. 28 ohm motherboardconductor 3609 is coupled to via 3610 and connector 3611. Connector 3611is coupled to 28 ohm module conductor 3612. 28 ohm module conductor 3612is coupled to connector 3613. Connector 3613 is coupled to via 3614 and28 ohm motherboard conductor 3615. 28 ohm motherboard conductor 3615 iscoupled to 28 ohm termination resistor 3616, which is coupled to ground3617.

FIG. 37 is a schematic diagram illustrating impedances for a bus whichsplits into multiple paths in accordance with an embodiment of thepresent invention. Driver 3701 provides an output that is split intoseparate paths, with one path going to RACPKG device 3702 and the otherpath going to RACPKG device 3703. These RACPKG devices may, for example,be components of a memory controller or interfaces for coupling a memorycontroller to a memory device. The outputs of RACPKG device 3702 andRACPKG device 3703 are merged and coupled to 14 ohm motherboardconductor 3704. 14 ohm motherboard conductor 3704 splits into multiplepaths, with one path coupled to via 3705, and the other path coupled tovia 3710.

Via 3705 is coupled to connector 3706. Connector 3706 is coupled to 28ohm module conductor 3707. 28 ohm module conductor 3707 is coupled toconnector 3708. Via 3710 is coupled to connector 3711. Connector 3711 iscoupled to 28 ohm module conductor 3712. 28 ohm module conductor 3712 iscoupled to connector 3713.

Connector 3708 is coupled to via 3709 and merges to 14 ohm motherboardconductor 3715. Connector 3713 is coupled to via 3714 and merges to 14ohm motherboard conductor 3715. 14 ohm motherboard conductor 3715 splitsinto multiple paths, with a first path coupled to via 3716 and connector3717 and a second path coupled to via 3721 and connector 3722.

Connector 3717 is coupled to 28 ohm module conductor 3718. 28 ohm moduleconductor 3718 is coupled to connector 3719. Connector 3722 is coupledto 28 ohm module conductor 3723. 28 ohm module conductor 3723 is coupledto connector 3724. Connector 3719 is coupled to via 3720 and merges to14 ohm motherboard conductor 3726. Connector 3724 is coupled to via 3725and merges to motherboard conductor 3726. Motherboard conductor 3726 iscoupled to 14 ohm termination resistor 3727, which is coupled to ground3728.

While FIG. 37 illustrates splitting and merging occurring outside of amodule, for example on a motherboard, such a configuration does notnecessarily serve to minimize the number of conductors needed to becoupled by connectors. Thus, it may be preferable to perform splittingand merging on a module, thereby reducing the number of conductorscoupled by connectors. Likewise, use of 14 and 28 ohm conductors doesnot necessarily maximize conductor density and conductor routingefficiency. Thus, it may be preferable to use other impedances, forexample, 28 and 56 ohms.

The values for impedances stated in reference to FIGS. 36 and 37 areexemplary. Embodiments of the invention may be practiced with variousimpedance values. Likewise, the number of paths that split from or mergeto buses may be varied. Moreover, FIGS. 36 and 37 provide examples ofpoints in the system where splitting and merging may occur. Anembodiment of the invention may be practiced with splitting and mergingoccurring at different points. For example, as illustrated in FIG. 34,splitting and merging may occur within a module. In such an embodiment,multiple paths are merged to single conductor, with the single conductorcoupled to connectors and a RACPKG device. However, as noted above,splitting and merging may alternatively occur at other points within thesystem.

Regarding FIGS. 34 to 37, to maintain signal integrity and impedancematching, signals should be applied to the non-split portion of the bus.For example, signals should be driven onto a bus either before a singleconductor is split into multiple paths or after the multiple paths havemerged into a single conductor. Also, the multiple paths should bematched so as to ensure equal propagation delay along each of themultiple paths split from a single conductor between the point where themultiple paths split and the point where the multiple paths arecombined. Matching the multiple paths is most readily done by matchingthe lengths of the multiple paths, although any technique that maintainsequal propagation delay may be used. Also, matching of propagation delayfrom the point where the multiple paths split to the points where themultiple paths reach devices coupled to the multiple paths may beperformed. Moreover, the propagation delays of different buses, forexample, address, control, clock, and/or data buses, may be matched tosimplify timing considerations of one or more devices coupled to thedifferent buses or multiple paths of one or more of the different buses.With appropriate delay matching and/or impedance matching, noise and/orinterference, for example reflection noise, can be minimized.

The modules and bus systems described with reference to FIGS. 21 to 26and 29 to 37 may be implemented using modules wherein the elementsdescribed for each module are disposed on at least one of a firstprimary surface and a second primary surface of the module. The elementsdescribed for each module may be disposed on the first primary surfaceand replicated to allow replicated elements to be disposed on the secondprimary surface. Thus, it is possible for the modules and bus systems toprovide twice the capacity of the single primary surfaces illustrated inFIGS. 21 to 26 and 29 to 37.

Other embodiments are also provided in accordance with the invention.For example, a module is provided wherein a first channel enters andexits the module, providing continuity from a point of ingress at afirst connector contact pin to a point of egress at a second connectorcontact pin and carrying a first signal, and a second channel enters themodule at a third connector contact pin, the second channel carrying asecond signal. The second channel is optionally connected to aterminator on the module. Entry and exit of the channels can occur atrespective connector contact pins. In preferred embodiments, the firstand second signals are “functionally equivalent”, wherein the termfunctionally equivalent in this context refers to the signals performingfunctions which are equivalent. The function of the first signal and thesecond signal would be equivalent if, for example, both signals functionto carry data information. In preferred embodiments, the function of thefirst signal is selected from one of the following functions: 1) carrydata information, 2) carry control information, 3) carry addressinformation, 4) carry data and control information, 5) carry data andaddress information, 6) carry control and address information, or 7)carry data, control and address information, and the function of thesecond signal is the same as the first signal. Stated another way, thesignals would be considered to be functionally equivalent if they areboth of the same type selected from one of the following types: datasignals, control signals, address signals, data plus control signals,data plus address signals, control plus address signals, and data pluscontrol plus address signals. It should be noted that a request bus orrequest channel may carry control signals, address signals, or controlplus address signals.

As another example of an embodiment in accordance with the invention, amodule is provided having two similar devices, wherein the term similarin this context refers to the devices being of the same type. Forexample, two devices would be considered to be similar devices if theyare both memory devices. A first channel is connected to the firstdevice, and a second channel is connected to the second device. Thefirst channel and the second channel carry functionally equivalentsignals, but have different topologies. Different topologies may resultfrom different routing patterns of the channels within the module. Thefirst channel is connected to a first contact, while the second channelis connected to a second contact and a third contact, wherein acontrolled non-zero propagation delay exists between the second contactand the third contact. The first channel is terminated on the module.The second channel may, but need not, be terminated on the module.Variations of this embodiment encompass modules wherein the first,second and/or third contact is replaced by a plurality of contacts.Other variations of this embodiment encompass modules wherein the firstchannel is coupled to a different number of contacts than the secondchannel.

As yet another example of an embodiment in accordance with theinvention, a system is provided having a first module and a secondmodule. A first channel enters and exits the first module and enters andis terminated on the second module. A second channel enters and exitsthe second module and enters and is terminated on the first module.

As a further example of an embodiment in accordance with the invention,a module is provided wherein a first request channel carrying a signalassociated with data enters the module at a third contact and terminateson the module, while a first channel carrying the data enters the moduleat a first contact and exits the module at a second contact.

As another example of an embodiment in accordance with the invention, asystem is provided having a first module and a second module, wherein afirst channel enters the first module on a first contact, exits thefirst module on a second contact, enters the second module on a thirdcontact, and terminates on the second module. A second channel entersthe second module on a fourth contact, exits the second module on afifth contact, enters the first module on a sixth contact, andterminates on the first module. Optionally, the first channel and thesecond channel carry functionally equivalent signals.

In preferred embodiments, a module such as those described above isadapted to be connected to a motherboard. There may be more than onemodule connected to a motherboard. A memory controller may be coupled toone or more modules. Collectively, the modules, motherboard, and/ormemory controller may form a system. Optionally, integrated circuits aremounted on modules, preferably memory integrated circuits.

While channel signals described above in reference to the various FIGS.are described as being provided to the modules and continuing until theyreach a terminator, it should be understood that the channels carryingthese channel signals are not necessarily unidirectional. Rather,channel signals may be communicated bidirectionally over the channels.For example, some channel signals may propagate from a memory controllerto a memory device and, ultimately, to a terminator, other channelsignals may propagate from a memory device to a memory controller (withthe possibility of an incident terminating wave propagating from thememory device to the terminator). Thus, either or both of the datachannels and request channels may be implemented as eitherunidirectional (in either direction) channels or bidirectional channels.Likewise, unidirectional and/or bidirectional communication may occurbetween various devices coupled to a channel, for example, between amemory controller, a first memory device, a second memory device, athird memory device, etc.

Terms such as enter, exit, ingress, egress, input, and output are usedfor clarity to denote aspects of a module or bus system that yield arelationship between modules, module slots, and/or other components, forexample, a controller. For example, signals from a controller can beunderstood to enter a module via an ingress connector and exit thatmodule via an egress connector. However, it should be understood thatsignals may pass in the opposite direction, entering via an egressconnector and exiting via an ingress connector. Additionally, under somecircumstances, for example, when signals originate on a module, thesignals may propagate along a channel in both directions, exiting themodule at both an ingress connector and an egress connector. Thus, termssuch as enter, exit, ingress, egress, input, and output should beunderstood to promote clarity, not to impose directional limitations onelements to which such terms refer.

References to a first channel and a second channel do not imply thatevery module of a bus system necessarily needs to have two channels.Likewise, references to a first, second, third, and fourth channel donot imply that every module of a bus system necessarily needs to havefour channels. Rather, modules having the same or different numbers ofchannels may be used together within the bus system.

The present invention may be used to implement a variety of embodiments,including modules comprising integrated circuits, modules comprisingmemory devices, modules comprising bus terminations, and modulescomprising conductors coupling one connector to another connector. Suchmodules need not be mutually exclusive; a module may include variouscombinations of such components. Moreover, such combinations may varybetween different channels. Examples of modules include, but are notlimited to, a module comprising an integrated circuit, a modulecomprising a bus termination, and a continuity module providingcontinuity between connectors of the module.

As illustrated in these examples, the present invention provides modulesadapted to be configured with one or more channels. While the foregoingexamples have been drawn to multiple channel embodiments, in every casea single channel may be implemented. The modules may be interconnectedusing various connectors to form bus systems. Such bus systems may beimplemented in a variety of configurations and channel definitions.Relative channel lengths may be reduced given a defined set ofconfiguration requirements. Bus interconnections within the system mayalso be reduced, thereby reducing the potential for impedance mismatchesand undesired channel loading.

As with many mechanical systems, the examples given above may bemodified in many ways. The use of right angle connectors has beendescribed, as well as the use of conventional connectors includingribbon and other flexible connectors. Other connector types may be usedwithin the present invention. Channel path definition, integratedcircuit layout, and internal bus routing on the various modules may alsobe readily adapted to suit the system designer's purpose.

Hence, the foregoing embodiments are merely examples. The presentinvention is not limited to these examples, but is defined by theattached claims.

What is claimed is:
 1. A module having first and second primary surfacesand having a first end, the module comprising: a first set of inputfinger connectors disposed on at least one of the first and secondprimary surfaces proximate to the first end; a first set of outputfinger connectors disposed on at least one of the first and secondprimary surfaces proximate to the first end; a second set of inputfinger connectors disposed on at least one of the first and secondprimary surfaces proximate to the first end; a second set of outputfinger connectors disposed on at least one of the first and secondprimary surfaces proximate to the first end; and a bus including a firstchannel extending from the first set of input finger connectors to thefirst set of output finger connectors and a second channel extendingfrom the second set of input finger connectors to the second set ofoutput finger connectors.
 2. The module of claim 1 further comprising atleast one first integrated circuit (IC) populating at least one of thefirst and second primary surfaces, the first channel connected to the atleast one first IC; and at least one second IC populating at least oneof the first and second primary surfaces, the second channel connectedto the at least one second IC.
 3. The module of claim 2, wherein thefirst IC and the second IC are memory devices.
 4. The module of claim 2,wherein the at least one first IC is a plurality of first ICs and the atleast one second IC is a plurality of second ICs.
 5. The module of claim4 wherein the first channel and the second channel allow simultaneousindependent access to at least some of the first and second ICs.
 6. Themodule of claim 2 further comprising: a third set of input fingerconnectors disposed on at least one of the first and second primarysurfaces; a third set of output finger connectors disposed on at leastone of the first and second primary surfaces; a fourth set of inputfinger connectors disposed on at least one of the first and secondprimary surfaces; and a fourth set of output finger connectors disposedon at least one of the first and second primary surfaces, wherein thebus further includes: a third channel extending from the third set ofinput finger connectors to the third set of output finger connectors;and a fourth channel extending from the fourth set of input fingerconnectors to the fourth set of output finger connectors.
 7. The moduleof claim 6, further comprising: at least one third IC populating atleast one of the first and second primary surfaces, the third channelconnected to the at least one third IC; and at least one fourth ICpopulating at least one of the first and second primary surfaces, thefourth channel connected to the at least one fourth IC.
 8. The module ofclaim 7 wherein the first channel, the second channel, the thirdchannel, and the fourth channel each allow simultaneous independentaccess to the respective ICs.
 9. The module of claim 6 wherein the firstset of input finger connectors, the first set of output fingerconnectors, the second set of input finger connectors, and the secondset of output finger connectors are disposed on the first primarysurface, and the third set of input finger connectors, the third set ofoutput finger connectors, the fourth set of input finger connectors, andthe fourth set of output finger connectors are disposed on the secondprimary surface.
 10. The module of claim 2 wherein the at least onefirst IC is a plurality of first ICs; the first channel has a firstcharacteristic impedance and is coupled to a plurality of paths, each ofthe paths is coupled to one of the first ICs, and the plurality of pathshas a combined effective impedance substantially equal to the firstcharacteristic impedance.
 11. The module of claim 6, wherein the firstset of input finger connectors, the first set of output fingerconnectors, the second set of input finger connectors, and the secondset of output finger connectors are disposed on the first primarysurface and the third set of input finger connectors, the third set ofoutput finger connectors, the fourth set of input finger connectors, andthe fourth set of output finger connectors are disposed on the secondprimary surface.
 12. A module comprising: a printed circuit board; afirst set of integrated circuits (ICs) mounted on the printed circuitboard; a second set of ICs mounted on the printed circuit board; a firstinput connector disposed on the printed circuit board proximate to afirst end; a first output connector disposed on the printed circuitboard proximate to the first end; a second input connector disposed onthe printed circuit board proximate to the first end; a second outputconnector disposed on the printed circuit board proximate to the firstend; and a first ingress bus coupled to the first input connector, thefirst ingress bus split into a first path and a second path, the firstpath coupled to the first set of ICs and the second path coupled to thesecond set of ICs, the first ingress bus having a first characteristicimpedance and the first path and the second path having a combinedeffective impedance substantially equal to the first characteristicimpedance.
 13. The module of claim 12 wherein the first path is coupledto a first terminator and the second path is coupled to a secondterminator.
 14. The module of claim 12 wherein the module furthercomprises: a first output connector disposed on the printed circuitboard; and a first egress bus coupled to the first output connector, thefirst path and the second path merged into the first egress bus, thefirst egress bus having a second characteristic impedance substantiallyequal to the first characteristic impedance.